1. Field of the Invention
The present invention generally relates to a method for manufacturing a metal structure in a multi-layer substrate, and more particularly to a method for manufacturing metal structures in a flexible multi-layer substrate.
2. Description of Prior Art
Miniaturization for all electronic productions is an unavoidable trend in this modern world. While the scales of the semiconductor chips continuously get smaller, the scale of the related technology for packaging needs to be microminiaturized to follow the scale of the semiconductor chip is also unavoidable. Today, because the integration of integrated circuits has been greatly increased, using a multi-layer substrate to package different kinds of chip devices is necessary to obtain a high performance integration system consequently. In the package technology industry, an etching method or build up process is a currently a commonly used method to manufacture a metal structure in a multi-layer substrate. Meanwhile, the higher the integration of semiconductor chip becomes, the higher the demand for finer metal structure.
Please refer to FIG. 1, which depicts a diagram of manufacturing a metal structure by an etching method according to the prior art. A metal layer is formed on a dielectric layer 100 of a multi-layer substrate. After a photoresist layer 104 is coated and exposed, the metal structures 102 are formed by an etching method. Generally, the metal structures 102 are formed by wet etching according to prior art. The side surfaces of the metal structures 102 are etched and undercuts happens thereto as shown in FIG. 1 because the isotropic character of the wet etching skill. Besides, the side surfaces become rough because of grain size of metal, especially of copper. With the increasing demand for finer metal structure brought by higher integration of semiconductor chips, an etching method now no longer can satisfy the needs for finer metal structure because of its drawbacks of the undercut and the roughness of the side surface.
Generally, copper can be used as the material of the metal structure when a multi-layer substrate is manufactured. It is easy to be corroded, especially when the polyimide is used to manufacture the dielectric layer. If a protective cover metal layer is desired to cover the metal structure's surface to prevent corrosion from other materials of the multi-layer substrate and to raise reliability of the metal structure, additional exposing and etching processes for forming the cover metal layers to cover the metal structure will be necessary according to the traditional etching method. The yield in manufacturing the multi-layer substrate is potentially decreased, due to issue of the positioning accuracy of the metal structure and the cover metal layer. Meanwhile, cost is also increased. Furthermore, the cover metal layer of covering the top surface, two side surfaces, even the under surface of the metal structure cannot be formed by one single photomask according to the etching method, i.e. the etching method cannot form the cover metal layer covering the metal structure completely to raise the reliability of the metal structure. The etching method cannot realize a metal structure as being a coaxial structure, either.
Please refer to FIG. 2A to FIG. 2D, which depict diagrams of manufacturing a metal structure by build up process according to the prior art. FIG. 2A shows a step of forming a very thin metal layer (seed layer) 102 on a dielectric layer 100 of the multi-layer substrate. FIG. 2B shows a step of forming a metal layer at the predetermined position (such as Electroplating) after coating a photoresist layer 104 except the predetermined position. FIG. 2C shows a step of removing the photoresist layer 104, and then the dielectric layer 100 and the metal layer 102 are left. FIG. 2D shows a step of etching the metal layer 102 to remove the metal material outside the predetermined position. However, the side surfaces of the metal structures 102 are etched as shown in FIG. 2 because the isotropic character of the wet etching process. Besides, because of the limitation of the size of the metal grain, the side surfaces of the metal structures become rough after the etching process.
Because of the limitation came of the size of the metal grain, either the etching method or the build up process cannot prevent the metal structure side surfaces from becoming rough. Such drawback can be a fatal restriction to the demand for finer metal structure. Furthermore, either the etching method or the build up process cannot form the cover metal layer of covering the top surface, two side surfaces, even the under surface of the metal structure completely by one single photomask to raise the reliability of the metal structure.
Therefore, there is a need to develop a method for manufacturing a metal structure in a multi-layer substrate and the structure thereof, so as to form the cover metal layer of covering the top surface, two side surfaces, even the under surface of the metal structure completely by one single photomask. The metal structure can be finer and with higher reliability and can be a coaxial structure.